The present invention relates to a laser equipped with an ultrasonic modulator and, more particularly, to a laser in which some light components of various wavelengths are extracted, modulated with ultrasonics, and emitted in a direction opposite to the incident beam.
Known types of apparatus in which some light components of various wavelengths are extracted, modulated with ultrasonics, and directed in a direction opposite to the original beam are shown in FIGS. 1 and 2.
The apparatus shown in FIG. 1 comprises a prism Q made of synthetic quarts, a prism P, a mirror M that totally reflects the light coming from the prism P, and an ultrasonic transducer TR mounted on one side of the prism Q. The transducer TR produces ultrasonic standing waves perpendicularly to the path of light. When the transducer TR is not in operation, only those wavelengths of light which are transmitted through the prisms Q and P and strike the mirror M at right angles retrogress in exactly the same path as the incident path, because of the reversibility of the path of light. Therefore, it can be said that this apparatus functions as a spectrograph. When the transducer TR is operated to produce ultrasonic standing waves S.W. within the prism Q, the light is diffracted, and the magnitude of the light is modulated.
The apparatus shown in FIG. 2 can function in a manner similar to the apparatus shown in FIG. 1. However, the functions of the prisms Q and P of the apparatus shown in FIG. 1 are performed by one prism PQ as shown in FIG. 2. Those wavelengths of light which vertically impinge on the total reflection mirror M of the apparatus shown in FIG. 2 are totally reflected and follow exactly the same path as the incident path in reverse. When the ultrasonic transducer TR of the apparatus shown in FIG. 2 is operated to set up ultrasonic standing waves S.W. within the prism PQ, light is diffracted, and the magnitude of the light is modulated. These known types of apparatus can be used to analyze light and modulate its magnitude.
FIGS. 3 and 4 schematically show ultrasonically modulated lasers equipped with the apparatus shown in FIGS. 1 and 2, respectively. In each of these lasers, a laser oscillation tube LT is mounted between the apparatus shown in FIG. 1 or 2 and an output mirror M'. Many optical elements of the conventional total reflection-type spectoral modulators employed in these lasers are exposed to air. Therefore, these apparatus may have the following problems: (1) Since the surfaces of the prisms are fouled, absorption takes place; (2) The apparatus are susceptible to the effects of the disturbance of air between optical elements; (3) It is difficult to adjust the relative positions between optical elements; and (4) The path of light may be varied by mechanical vibration. Hence, the oscillation of the lasers lacks stability.